The present disclosure relates generally to methods of measuring hydrogen sulfide concentrations in reservoir fluids. More specifically, in certain embodiments, the present disclosure relates to chemical probes useful for measuring hydrogen sulfide concentrations in reservoir fluids and associated methods and systems.
The presence of hydrogen sulfide is a common occurrence in a number of subsurface hydrocarbon reservoirs. The presence of hydrogen sulfide may be problematic, as it can be highly corrosive to casing, tubing, and other metallic and polymeric tools. Special care may need to be taken in recovering hydrocarbons from hydrogen sulfide containing reservoirs. As such, it is useful to determine the presence and concentration of hydrogen sulfide content of reservoir fluids before production begins.
Currently, the concentration of hydrogen sulfide in reservoir fluids is typically measured by analyzing samples captured using down hole fluid sampling tools. Two examples of downhole fluid sampling tools are the Modular Dynamics Tester from Schlumberger and the Reservoir Description Tool from Halliburton. These tools and methods of using them and other methods and tools are described in U.S. Pat. Nos. 6,223,822, 6,469,636, and 7,128,144, the entireties of which are hereby incorporated by reference.
Briefly, conventional downhole fluid sampling tools are lowered into a wellbore and used to collect reservoir fluid samples downhole in a sample container. The fluid from the sample container may then be transferred into smaller storage bottles which are shipped to a laboratory for hydrogen sulfide analysis using a sulfur chemiluminescence gas chromatography detector and/or a Draeger tube. One problem with these conventional methods it may take several weeks or months for the sample container or storage bottles to be transported to the lab and have the analysis completed. During that time, fluid present in the sample container or storage bottles may undergo drastic pressure and temperature changes. As a result of these changes and other factors, the hydrogen sulfide present in the sampling container or storage bottle may undergo irreversible transformations. Thus the amount of hydrogen sulfide measured in the laboratory may not accurately reflect the concentration of hydrogen sulfide present in the subterranean formation. Also, the presence of brine and oil phases in the sample may skew the hydrogen sulfide equilibrium in the sample thus further skewing the laboratory analysis of the sample. Furthermore, conventional storage bottles must be reheated and re-pressurized in the laboratory, however due to variation in the fill levels of storage bottles, the analysis of hydrogen sulfide may not accurately represent the reservoir fluid characteristics.
It is desirable to develop a method of measuring hydrogen sulfide concentrations in reservoir fluids that does not suffer from any of these conventional drawbacks.